The present disclosure relates to anchoring elements and articular surfaces for human or veterinary implants. The disclosed anchoring elements are useful in situations where exposure is difficult, the implantation trajectory is oblique to the implantation site, or the implantation site is tapered, conical, or wedge-shaped. For example, the disclosed anchoring elements are useful in the context of a glenoid implant for shoulder arthroplasty, so that the preparation of the glenoid and implantation of the glenoid component take place along an oblique surgical access and implantation trajectory. An oblique approach, or an antero-lateral approach, to the glenoid is technically simpler and less invasive than a lateral trajectory to the glenoid. This disclosure is made in the context of a glenoid component for shoulder arthroplasty for the purpose of illustrating the relevant principles of the technology.
In total shoulder arthroplasty, a glenoid implant is attached to a prepared glenoid or scapula, and a humeral implant is attached to a prepared humerus. The humeral implant usually includes a ball or convex articular surface at a proximal end thereof which engages and moves relative to a socket or concave articular surface formed in a lateral aspect of the glenoid implant, although this arrangement is sometimes reversed so that the humeral implant includes the convex articular surface and the glenoid implant includes the convex articular surface. The ligaments and muscles of the shoulder surround the implants and maintain the humeral implant against the glenoid implant, while at the same time allowing relative movement therebetween.
Current implants frequently have a central peg or keel, occasionally with two or three small peripheral supporting pegs. These implants rely on the centrally placed anchoring element to provide the majority of the fixation. In situations where the surgeon encounters bone defects, bone cysts, or where a prior component has been removed, there is often a central defect in the bone where fixation is not possible.
Current instruments for standard glenoid arthroplasty, including drill bits, reamers, and trial implant components, and final implant components are frequently designed for the surgeon to approach the scapula along a direction perpendicular to the face of the glenoid portion of the scapula; this may be referred to as a direct lateral trajectory. However, the standard incisions and safest surgical approach for glenoid arthroplasty provide exposure for the surgeon which is more oblique, or antero-lateral. In order to facilitate the insertion of instruments perpendicular to the face of the glenoid, the surgeon may find it necessary to resect the articular portion of the humeral head and forcefully retract the patient's skin, muscle and remaining humerus out of the way posteriorly to obtain adequate exposure. In doing so, the surgeon may potentially injure nerves or blood vessels. Often the surgeon will purposely cut the biceps tendon or portions of the pectoralis major tendon to improve exposure to facilitate this step, as well as releasing the glenohumeral ligaments. All of this dissection, retraction, and removal of bone and soft tissue is done in order to allow the surgeon enough room to implant the glenoid prosthetic component.
Thus, there is a need for an implant anchoring mechanism that can be inserted from an oblique angle to allow for a less invasive and technically simpler surgical operation, for example, for anchoring a glenoid prosthetic component to scapular bone.
The present disclosure sets forth an oblique-insertion anchoring mechanism for securing a glenoid prosthetic component to scapular bone. The anchoring mechanism can be inserted from an oblique angle to allow for a less invasive and technically simpler surgical operation. The anchoring mechanism is formed from a rounded dowel which projects from the medial aspect of a glenoid prosthetic component. The dowel projects at an angle which is not perpendicular to, or normal to, the medial side of the glenoid component, but is instead an acute angle less than 90 degrees. In the acute angle between the dowel and the medial side of the glenoid component there is a triangular reinforcement plate which buttresses the dowel and arises at a supplementary angle from the medial side of the glenoid component. The dowel and the edge of the reinforcement plate meet at the apex of the triangle.
It is contemplated that the number and location or placement of the anchoring elements will vary to accommodate different clinical situations.
The anchoring elements disclosed herein may be placed peripherally in a ring orientation, avoiding a bony central defect. Anchoring elements placed more peripherally provide more resistance to the effects of shear forces caused by the pressure of the humeral head during edge loading, as the distance and resultant lever arm decrease.
Biomechanically, the triangular arrangement of the dowel with the reinforcement plate allows the anchoring element to stabilize the body of the prosthesis from both legs of the triangular base to protect against both anterior and posterior eccentric forces. The triangular base of the anchoring element provides balanced anchoring to resist the anterior and posterior directed forces. The disclosed technology has fixation at both legs of the triangle, symmetric in distance from the edges of the body of the prosthesis, and all along the base of the triangle as well. The triangular shape also provides much larger surface area to resist superior and inferior directed forces than pegs alone. This is in contrast to a simple obliquely oriented peg which places the point of fixation of implant off center, allowing liftoff at the side farthest from the peg.
The disclosed design of the anchoring element may be even more preferable than traditional designs when glenoid deformity is present. Glenoid retroversion and glenoid vault bone loss are commonly seen in cases of advanced arthritis and the present design better fits the bony anatomy in these cases. This technology may also be preferable for revision glenoid arthroplasty operations.
The anchoring elements disclosed herein allow the prosthetic component to be inserted at an oblique angle. Therefore, there is less need to forcefully retract bone or soft tissues to obtain adequate exposure. The surgeon may be able to implant the prosthetic component without cutting the pectoralis major, the biceps tendon, or the glenohumeral ligaments. These tendons and ligaments serve as static and dynamic stabilizers of the humeral head during normal motion. If left intact, humeral motion remains more controlled and centered, reducing the incidence of humeral translation and contact with the far peripheral edges of the glenoid component. Reducing edge-loading results in less loosening forces transmitted to the anchoring elements, which is a common mode of failure of glenoid prosthetic components and total shoulder arthroplasty overall. Furthermore, the surgeon may not be compelled to resect the humeral head and may choose instead to use a bone-preserving humeral resurfacing arthroplasty component during the operation, which may further reduce operative time, blood loss and bone removal.
The inferior chamfer design of the lateral bearing surface of the glenoid component minimizes the incidence of impingement between the humeral component and the inferior articular margin of the glenoid prosthesis, thus reducing the likelihood of implant loosening and wear. Humeral impingement on the inferior glenoid is reported to be a cause of implant loosening and wear. Retrieval studies of loose failed glenoid implants have repeatedly demonstrated deformation at this inferior location.
For at least these reasons, the disclosed technology may simplify the operation, shorten the length of the operation, reduce soft-tissue dissection, reduce risk of neurovascular injury, reduce blood loss, reduce the need for bone resection, and may improve implant longevity.
Preservation of soft-tissues in glenoid preparation, optionally combined with the use of a humeral resurfacing component, may make shoulder arthroplasty more appealing for younger patients with significant degenerative disease, a patient group currently generally discouraged from undergoing shoulder arthroplasty.
An objective of the technology is to disclose a unique positioning of a dowel with planar buttress element in a glenoid prosthetic component.
Another objective of the technology is to disclose an improved glenoid prosthetic component that permit placement of anchoring elements in locations to better replicate normal human anatomy.
Yet another objective of the technology is to disclose an improved glenoid component that is inserted obliquely.
Yet another objective of the technology is to disclose an improved glenoid component having a dowel designed to match the specific anatomic shape of the surrounding bone.
Yet another objective of the technology is to disclose an improved glenoid prosthetic component having unique differential radius of curvature in the superior-inferior and anterior-posterior directions.
Yet another objective of the technology is to disclose an improved glenoid prosthetic component having a unique inferior chamfer.
Other objectives and advantages of this technology will become apparent from the following description taken in conjunction with the accompanying drawings which illustrate examples of this technology. The drawings constitute a part of this specification and include examples of the present technology and illustrate various objects and features thereof.